Actually, Leeuwenhoek's field was dry goods merchant. He was a gifted amateur, like essentially all scientists of his day.
Darwin's job was primarily to hold the social status to keep the captain company at dinner. However, as naturalist, he was intended to discover things that would bring glory to the Empire. The Theory of Evolution certainly qualifies.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"